Fix build workflow

Author: jtpio

.github/workflows/build.yml

@@ -2,7 +2,8 @@ name: Build
 
 on:
   push:
-    branches: main
+    branches:
+      - main
   pull_request:
     branches: '*'
 
@@ -14,7 +15,7 @@ jobs:
       uses: actions/checkout@v2
 
     - name: Base Setup
-        uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
+      uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
 
     - name: Install dependencies
       run: python -m pip install -U jupyterlab~=3.1 check-manifest